Help deciding between zoned furnace/ac vs mini splits in existing home without ducting

bryantroll

Hoping for some help in choosing an all new heating and cooling solution for a major home rehab where there is no existing HVAC system currently. (There was a 40 year old SolaRoll hydronic in-floor heating system but both the tubing and the boiler have failed and is being abandoned.) Heating is necessary, AC is a big bonus.

I think I've narrowed things down to mini splits for each bedroom plus each common area (4-zone and 3-zone), or a variable speed ducted 2-zone furnace/AC system (basement unit and main unit). If there's something else you recommend, I'm all ears.

I'll try to list bullet points to get the main info out there:

Climate:
--location: Evergreen, CO (outside of Denver)
--Coldest month (avg.): 42 F high, 9 F low (*we had 3 days with a low of -15 F overnight this winter)
--Warmest month (avg.): 79 F high, 49 F low (but it does get hotter some days)
--humidity: 40%-70%

Home Info:
--monolithic (concrete) dome, built in 1982, split into 2 units
--2" thick concrete exterior walls covered in 3" spray foam - should be quite efficient
--basement unit is 1600 sq. ft. with 2 beds and 2 baths and ground level walkout
--main floor and loft is 2300 sq. ft. with 3 beds and 3 baths
--I do have natural gas service so it is an option

Notes:
--I need at least 2 separate zones for basement and main units
--I plan to own long term so looking at this as a long term investment
--Basement does not appear to have a vapor barrier or insulation currently so I need to solve this
--House is mostly stripped down to the studs right now so deciding on HVAC has to happen before anything else
--If I go ducted, ducting will reduce ceiling height in basement bedroom spaces
--If I go mini splits, an electrical system upgrade is needed (~$3,000 extra)
--Cost / benefit analysis for each system to help decide which way to go!

I would like to DIY install with the help of a friend who has experience as an HVAC installer in the past. Ideally, I would hire help with system design and then I could take care of the install of the system.

Possible to spitball rough costs for each option?
Other pros/cons?

I can share floor plans or any other info you need if it helps.
Also if there is someone local to the Denver area who can help plan out a good quality yet cost effective solution, please let me know!

HVACNUT

bryantroll said: Possible to spitball rough costs for each option? 

There's no spitballing any prices. That you work out with your contractor and your accountant. 

I'd go with another boiler, radiant throughout again, a separate 2 zone AC system with a hydro coil for second stage heat if needed. 

A lot of people are going towards ductless as the only heat source, but I like knowing that if a part goes bad, I have it in my van or my supplier will have it at the "will call" counter. 
Maintenance is a must and repairs can be pricey even if parts are under warranty as opposed to a simple boiler service or repair.

Ironman

Has a Manual J heat loss calculation been done to determine the actual load and what type of equipment can supply the need?

There’s a whole lot more to installing mini splits than the internet peddlers let on. 

Hot_water_fan

Neither option: I’d do a ducted heat pump with furnace backup, which shouldn’t cost much more than AC+furnace. You’ll be able to use the heat pump nearly the entire time and have the furnace just in case. I’d recommend variable speed if you can, I have it and it’s silent. Basically, my heat pump is on all winter, like simmering something on the stove. 

You could do the ducted heat pump with resistance backup instead of the furnace, but that might require the electrical upgrade you mentioned. It depends on the heat loss of course. 

I would definitely NOT consider a ductless head in every bedroom. If you weren’t doing any other work on the space it might make sense, but you are, so do it right. 

Jon_blaney

So some questions: How do the cost for gas and electric compare? Looks like the needs will be different for the basement unit and the main unit. Have you considered different systems for each? What is the long term plan for the rental unit? Who pays for the utilities? Will the rental price cover the cost of a more expensive system like heat pumps?

random12345

@bryantroll I'll be interested to see how this turns out for you and what the pros on here recommend. I'm just a homeowner, not an installer. Xcel Energy appears to be your electric and gas supplier. Is that correct?

bryantroll

HVACNUT said:

bryantroll said: Possible to spitball rough costs for each option? 

There's no spitballing any prices. That you work out with your contractor and your accountant. 

I'd go with another boiler, radiant throughout again, a separate 2 zone AC system with a hydro coil for second stage heat if needed. 

A lot of people are going towards ductless as the only heat source, but I like knowing that if a part goes bad, I have it in my van or my supplier will have it at the "will call" counter. 
Maintenance is a must and repairs can be pricey even if parts are under warranty as opposed to a simple boiler service or repair.

Thank you for taking the time to reply.
There's no "radiant is the most expensive, mini splits are in the middle, forced air is the least expensive"?
Also yes I would love radiant heat plus AC, but what kind of budget are we talking about here?
I'm looking for advice on a good middle of the road, great value, bang for the buck solution. Maybe I'm wrong but sounds like you're talking about the open checkbook deluxe $$$ solution. Or am I misunderstanding? Always easy to spend someone else's money, but this is my own tight budget I'm managing here .
Another interesting thought -- depending on what I use, I could do heat on both units, and just AC in the main upstairs unit. The basement likely won't need much for AC.

Ironman said:

Has a Manual J heat loss calculation been done to determine the actual load and what type of equipment can supply the need?

There’s a whole lot more to installing mini splits than the internet peddlers let on. 

The original drawings from 1982 had some heat calculation info on them but I have not done a Manual J myself -- any recommendations on how I find someone who can do a good job on that, or just head to Google for it? Sounded like it was $700+ for this so considering I need to keep a tight budget I wasn't sure if it was absolutely essential, but I have a feeling I know what your recommendation will be. Thanks for your input!

Hot_water_fan said:

Neither option: I’d do a ducted heat pump with furnace backup, which shouldn’t cost much more than AC+furnace. You’ll be able to use the heat pump nearly the entire time and have the furnace just in case. I’d recommend variable speed if you can, I have it and it’s silent. Basically, my heat pump is on all winter, like simmering something on the stove. 

You could do the ducted heat pump with resistance backup instead of the furnace, but that might require the electrical upgrade you mentioned. It depends on the heat loss of course. 

I would definitely NOT consider a ductless head in every bedroom. If you weren’t doing any other work on the space it might make sense, but you are, so do it right. 

Thanks for your input. If I do ANY heat pumps at all, the electrical upgrade is required. Why do you suggest that the ductless systems in bedrooms is inferior? Genuinely interested in learning pros and cons.

Jon_blaney said:

So some questions: How do the cost for gas and electric compare? Looks like the needs will be different for the basement unit and the main unit. Have you considered different systems for each? What is the long term plan for the rental unit? Who pays for the utilities? Will the rental price cover the cost of a more expensive system like heat pumps?

The upstairs would benefit from heat and AC, while the basement could likely just use heat and not really have a need for AC.
It looks like I pay about 80 cents / therm based on my last gas bill plus a $10 monthly service charge, so with my HWH just idling and no other gas use I paid $14 for 3 therms last month.
It looks like my electric is about 12 cents / kWh plus a $14 monthly service charge, so I paid $94 for 640 kWh last month. This was just running a couple electric space heaters and some power tools and lights.
The property should rent for a pretty good amount upstairs and I will personally live in the basement. I will be paying the utility bills, and I hope to own the property a long time so monthly costs are definitely a consideration.

random12345 said:

@bryantroll I'll be interested to see how this turns out for you and what the pros on here recommend. I'm just a homeowner, not an installer. Xcel Energy appears to be your electric and gas supplier. Is that correct?

Hope it helps! I actually have Xcel for gas and CORE for electric at my location.

Hot_water_fan

Thanks for your input. If I do ANY heat pumps at all, the electrical upgrade is required. Why do you suggest that the ductless systems in bedrooms is inferior? Genuinely interested in learning pros and cons. 

I’m curious, does the AC + furnace also require an electrical upgrade? I would install the same exact AC unit, just the heat pump version, so no upgrade necessary unless the AC needs it. The amps should be the same - in lieu of electric resistance, the furnace would function as the cold weather backup. If the AC requires the upgrade, then you could consider that the cost of AC. There’s a strong case to be made for sizing the heat pump for the cooling load and covering the heating shortfall with the furnace. 

As to the ductless - they’re inferior for a handful of reasons. 

1. They’re almost always extremely oversized. That’s because the smallest is usually around 6kbtu, which is too big for most bedrooms. This leads to excess turning on/off, so more noise, more wear and tear, and worse temperature swings. I’ll come back to this one. 

2. They can’t dehumidify well - maybe not as important in CO, but a main drawback other places. 
3. They don’t serve a filtration role well - their filters are porous and to clean, you have to service every head compared to 1 central, higher quality filter. 

4. It’s clunky to incorporate backup, which you’ll need if you’re under -15 F. You’d need to run electricity/ducts/tubing to every room, which is the bad kind of redundant. 

5. The sizing is especially bad when it’s a system with 1 outdoor unit connected to multiple indoor units. The outdoor units that can do this have poor modulation and it gets worse the more units you attach, somewhat unexpectedly. Units that are 1 outdoor to 1 indoor unit can modulate better, but then you have many more outdoor units. The oversizing of the outdoor unit leads to really poor efficiency. 

6. If you’re introducing fresh air, you can’t do it with the ductless. A ducted unit could be configured to allow ventilation. 

There's no "radiant is the most expensive, mini splits are in the middle, forced air is the least expensive - ~$40k, ~$30k, or ~$20k"? I'm just trying to make an informed decision but am still trying to figure out how to get property informed.

The radiant + AC will be the most expensive option by far - you’re installing two parallel systems instead of using the ductwork for both. Radiant alone is usually the more expensive option. 

random12345

Anytime someone asks about what kind of system they should install, that's an excuse for me to go looking at stats and trends, and I enjoy doing that, but please take all of this with a big grain of salt. For me, this is a fun way to learn more about HVAC, but for you, it's a major financial decision. Operating costs are a major factor here in terms of whether to go fully electric or go with gas. There are 2 questions that need answering in my mind: 1) What are your current prices for gas and electricity? 2) How will these change relative to one another in the future? For the first, the Xcel website has their gas rates going back to 2017. I plotted it out:
https://xcelenergy.com/company/rates_and_regulations/rates/rate_books

CORE doesn't publish past rates, but here is their rate structure:
https://core.coop/my-cooperative/rates-and-regulations/rate-structure/
You should check this against your gas and electric bills to make sure there aren't any additional hidden charges. The current price of electricity from CORE looks like it's $0.11627/kwh plus a monthly demand charge of $2 x max electric demand in kW, plus a wholesale power cost adjustment of $0.00302, for a total of $0.11929. Gas is $0.8264/therm, and since 2019 has ranged from $0.38-$1.42/therm. The high rates happened in late 2022, and prices have dropped a lot since then. Electric rates seem to have been more stable. This calculator is a useful starting point for predicting what your energy costs may be with various heating systems:
https://efficiencymaine.com/at-home/heating-cost-comparison/
You can plug in different prices and change parameters using the "Show Details" check box. Under current prices, the ductless heat pump appears to be 17% more expensive to operate than the gas furnace. The ducted heat pump is 47% more. I'm assuming equivalent heat load for all options, furnace efficiency of 93%, ductless and ducted heat pump efficiency of 270%, and distribution efficiency of 80% for furnace and ducted HP and 100% for ductless HP. At its peak of $1.42/therm, the furnace would have been 47% more, whereas at its low point of $0.38/therm, it would have been 64% less than the ductless HP. During the shoulder seasons, if we assume a higher efficiency of 350% for the HPs, then the ductless HP is about 10% cheaper, but ducted is still 13% more expensive than the furnace. The electric demand charge will also add to your monthly bill if you fully electrify your heating, especially if you're paying for the tenant's heat as well as your own. The additional demand charge cost would depend on the heat pump vs furnace power draw between 4-8 PM in the heating season. If it's an additional 5 kW, then that's an extra $120/yr for the HPs, but could be more. I'm guessing the AC vs ducted/ductless heat pump power draw difference during Summer would probably be negligible, and so wouldn't result in a big change to your demand charge. The gas boiler would probably be the cheapest option to operate because it has a higher distribution efficiency. Insulating the hot water pipes everywhere but the living spaces would increase the distribution efficiency and lower costs further. On the other hand if you electrify everything and get rid of gas service entirely, you would save an additional $136.56-201.24 on the gas monthly service charge, whereas you would never be able to eliminate the monthly electric charge. You would also need to get a heat pump water heater in that case, and that would be more expensive than gas to operate as well (https://efficiencymaine.com/at-home/water-heating-cost-comparison/) I'm just looking at operating costs here. Installation and equipment costs are the other factor. @Hot_water_fan's suggestion to install a HP instead of AC does not make sense to me, given that it will probably be more expensive to operate than the furnace even during the shoulder seasons. A ducted HP would need to be 400% efficient to achieve cost parity with the furnace...seems unlikely. More thoughts to follow...

EDIT: Made a couple mistakes, now corrected.

Hot_water_fan

@random12345 the thought is that if you installed a ducted HP + furnace for a trivial amount more than a ducted AC + furnace, why not take the cheap insurance policy? Instead of tied to just on-site gas, you can use on-site gas, off-site gas/coal/wind/solar/nuclear, etc. It provides more options for an uncertain future, since none of us have a clue what future prices will be . 

random12345

@bryantroll I've been looking at historical temperature averages for Evergreen, and I'm wondering if you even need A/C?
https://weatherspark.com/y/3535/Average-Weather-in-Evergreen-Colorado-United-States-Year-Round
If you google around, one forum I saw most people commented that A/C wasn't necessary.
https://city-data.com/forum/denver/594590-c-evergreen.html
Looks like only July and August gets a bit warm in the afternoons, but since it's near 0% humidity, you might be able to get by comfortably if the house has some shade and using an evaporative cooler like someone on that forum suggested. https://nytimes.com/wirecutter/blog/do-swamp-coolers-work/

@Hot_water_fan That's true and a good point. If gas prices temporarily spike like they did last year, then in theory you could use the heat pump. Two potential counterarguments to that are 1) HP is more expensive than the A/C upfront, potentially a couple thousand, so not that cheap as insurance and 2) Because HP COP (or energy factor, EF) can vary by brand/unit, and outside temperatures, how would you know when it's worth it to turn off the furnace and switch to the HP? If it's 40 F outside, the COP could be anywhere from 2 to 3. If the gas price is back to $1.42/therm, you would need to know for sure or might be shooting yourself in the foot...If only there were an easy way to measure the HP EF in real-time...At the same time, high efficiency gas furnaces may not deliver as advertised either if installed or configured incorrectly.
https://swenergy.org/wp-content/uploads/heat-pump-study-2022.pdf
https://aceee.org/sites/default/files/publications/researchreports/a1602.pdf
https://mncee.org/cold-climate-air-source-heat-pump-field-assessment
https://nrel.gov/docs/fy15osti/63702.pdf

Hot_water_fan

Oh yeah for thousands more, not worth it. When I priced it, the heat pump was ~$50 more. Surely prices will vary, but a heat pump is essentially identical to an AC unit so the premium should be low. You could experiment to find costs vs temps but frankly that’s probably more effort than it’s worth. Change over at 15 degrees and roll.  

random12345

The more heat pump field performance studies I read, the more convinced I am that it's difficult to know for sure what their real-world efficiency actually will be. So much depends on the installation. Brand and model also have an impact. I'm thinking the COP range is probably somewhere between 2-3.5. Most likely it's 2.5-3 from what I've read. For a 95% furnace the equivalent actual AFUE would be anywhere from 79%-95%. That's quite a big swing. I read a study showing that ductless HPs outperformed ducted. Another found that the type of refrigerant has an impact. Recently DOE revised how HPs are rated, switching from HSPF to HSPF2 because the original rating exaggerated actual performance. Purely from an operating cost standpoint, at these prices I think the gas boiler and furnace win. If he does as you suggest, and depending on the system, the price of gas would have to be much higher than it is now to guarantee savings. The uncertainty makes it unattractive. Manufacturers don't seem to publish their lab data either concerning COP performance vs outdoor temperature. That would certainly help narrow things down a bit. Is forced air cheaper to install than hot water baseboard or radiators? If he gets the forced air with a gas furnace and no A/C, he can always install a heat pump later.

Hot_water_fan

 Is forced air cheaper to install than hot water baseboard or radiators? If he gets the forced air with a gas furnace and no A/C, he can always install a heat pump later. 

I don’t think a boiler makes any sense in a budget sensitive application when someone wants AC . 

I hear your concerns, @random12345, I just think it’s so cheap to install a ducted HP vs a ducted AC, may as well leave the option open. Maybe you use it a lot, maybe not. 

Where I live, the issue isn’t the cost of the gas molecules (that’s forever changing, sometimes cheap, sometimes not), but the cost of delivering those molecules, which is a variable cost here. Each utility bills differently, but I like the flexibility to avoid costs like that. It’s hard to imagine a world where my gas delivery rate ever decreases, even if the gas itself does, since those cost drivers are maintenance related. Right now, we’re at $.75/therm just delivery. I know other gas utilities do it differently, charging a high monthly fee, which starts making oil and propane look good. 

random12345

Yes all fair points. If the HP is not much more than the AC as you say, then you've convinced me. I don't see why anyone wouldn't do it. If he leaves out the AC though, he has maybe more room in the budget and can spend that on a hydronic system which is more expensive to install but cheaper to operate and maybe more comfortable than the forced air options. If radiant is not an option, would you choose hot water baseboard or stand-alone radiators in that instance?

Hot_water_fan

Eh I doubt hydronic wouldn’t be noticeably cheaper to run - new ECM blowers use little energy and many efficient boilers need primary/secondary piping and have high head loss. Probably ends up being a wash distribution-wise. 

Baseboard or radiator are both fine, if return temps are similar. 

random12345

Tough to make those air ducts leak-proof though.

bryantroll

@Hot_water_fan ,
I wouldn't need the additional electrical upgrade if I used a gas furnace for my heat source. The heating requirements are substantially more than the cooling requirements, so even if I had AC in the summer it wouldn't push me over the limit so that I require the additional electrical upgrade. I'm not against the extra $3000 for the electrical upgrade, its just one weight in the scale when factoring in cost/benefit.

Thank you for explaining the drawbacks you see in ductless mini splits. Even if they are oversized, doesn't the variable speed compressor give them quite a bit of leeway in self-downrating their operation? I believed this allowed them to manage smaller spaces and optimize efficiency, within reason (ex: a 6k unit in a room that requires 4.5k)

If I did ductless mini splits I would have them in the common area plus each bedroom, which is limited in that its not multiple supplies in the large space, and also no conditioning in the bathrooms. Not absolute dealbreakers, but one of the reasons that running ducting has an advantage.

I honestly think that at this point I'd prefer to run ducting for many of the reasons you mentioned, but it would need to be 2 separate zones (basement zone and main/2nd floor zone). My concern is that I just don't know how headroom space I will lose to run this ducting in the basement which is a finished separate unit and I want to keep as comfortable as possible -- full ceiling height is about 90" currently. There is a 9" wide glue lam that sticks down 13" from the ceiling that you walk under to get into each basement bedroom. The ducting would run alongside this glue lam just inside the bedrooms so it would extend that low ceiling height out -- I don't know how tall or how wide that soffit would need to be.
My secondary concern is how initial costs compare for this system, and then of course cost savings over time to operate the units.

I think my next step is to find a good HVAC guy in the area who can help propose a ducted system and what it will need. I'm guessing the correct way to do this is to have a manual J done, and then work on system design? Ideally I'd find an expert to handle these things who is ok with handing off the install to me at that point, not sure how common that is to find.

Hot_water_fan

Thank you for explaining the drawbacks you see in ductless mini splits. Even if they are oversized, doesn't the variable speed compressor give them quite a bit of leeway in self-downrating their operation? I believed this allowed them to manage smaller spaces and optimize efficiency, within reason (ex: a 6k unit in a room that requires 4.5k)

Surprisingly, no. When it’s a multi-split (one outdoor unit connected to many indoor units), the turndown is extremely limited. Often the best the outdoor unit can do on paper is about 50%, but the indoor units will be substantially oversized, so it’s much less in practice. For example, a 1-to-3 24kbtu Mitsubishi hyper heat can only turn down to 11kbtu at 47F. If the three rooms only have a heat loss of about 20btu/sqft x 3 x 200sqft = 12kbtu at 5F, then it can’t help but short cycle. 

It’s different for 1-to-1 setups - they can actually modulate.